This invention relates to a liquid phase epitaxy (LPE) technique and in particular to a means for growing garnet film on a plurality of substrates simultaneously.
Liquid phase epitaxy for growing magnetic garnets utilizing a technique of dipping non-magnetic substrates in a supersaturated solution to provide large area films for bubble domain devices is old. An article entitled "The Growth of Magnetic Garnets by Liquid Phase Epitaxy" by Blank et al, Journal of Crystal Growth, Vol. 17, pp. 302-311 of 1972 discusses a substrate vertically fixed on a substrate holder and lowering the substrate into a crucible having a melt and rotating said substrate while in said melt. The article entitled "Liquid Phase Epitaxial Growth of Magnetic Garnet Films by Isothermal Dipping in a Horizontal Plane with Axial Rotation" by Giess et al, Journal of Crystal Growth, Vol. 17, No. 1, October 1972, pp. 36-42 discusses the dipping of substrates disposed horizontally on a substrate holder and rotating the same in a horizontal plane while in the dip. And the U.S. Pat. No. 4,092,208 to Brice et al also discusses dipping a vertically disposed substrate in a crucible having a suitable melt. The patent also discusses dipping a horizontally disposed substrate into the melt and rotating the same in a horizontal direction.
However, the foregoing methods of growing garnet film on substrates has been found to be deficient where the processing of a plurality of wafers at one time is involved--the so-called batch processing of wafers.
Wafers produced in such a batch process have been found to vary from wafer-to-wafer in film thicknesses beyond acceptable tolerances and the films themselves on each of the wafers have been found not to be uniform, i.e., there was no uniformity in the thicknesses of the film from the middle of the wafer to the periphery thereof. Since the thickness of the film and its uniformity has a definite affect on the magnetic properties of the wafer, the wafers had to be separated according to their film thicknesses and their uniformity so that a plurality of wafers and the chips formed therefrom, when used together, would have the same magnetic properties.
Accordingly, it is a principle object of this invention to provide a method by which a plurality of wafers may be processed at one time yet provide film thicknesses wafer-to-wafer within acceptable ranges and provide a film of uniform thickness on each wafer.